Solid ink or phase change ink printers conventionally receive ink in a solid form, sometimes referred to as solid ink sticks. The solid ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a printhead assembly for jetting onto a recording medium. The recording medium is typically paper or a liquid layer supported by an intermediate imaging member, such as a metal drum or belt,
A printhead assembly of a phase change ink printer typically includes one or more printheads each having a plurality of ink jets from which drops of melted solid ink are ejected towards the recording medium. The ink jets of a printhead receive the melted ink from an ink supply chamber, or manifold, in the printhead which, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each ink jet includes a channel having one end connected to the ink supply manifold. The other end of the ink channel has an orifice, or nozzle, for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture, or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators in the ink jets to expel drops of fluid from the ink jet nozzles onto the recording medium. By selectively activating the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
One difficulty faced by fluid ink jet systems is partially or completely blocked ink jets. Partially or completely blocked ink jets may be caused by any of a number of factors including contamination from dust or paper fibers, dried ink, etc. In addition, when the solid ink printer is turned off, the ink that remains in the print head can freeze. When the printer is turned back on and warms up, the ink thaws in the print head. Air that was once in solution in the ink can come out of solution to form air bubbles or air pockets that can become lodged in the ink pathways of the print head. Partially or completely blocked ink jets can lead to ink jet malfunctions or failures resulting in missing, undersized or misdirected drops on the recording media that degrade the print quality. When a jet failure cannot be recovered by a print head maintenance action, the result is a permanent or chronic weak or missing (CWM) jet failure. CWM jet failures may require the replacement of an entire print head or section of the print head that includes the CWM failure(s).
Temporary jet failures, also called intermittent weak or missing (IWM) jet failures are caused by a number of different factors including but not limited to those described above for a CWM. These IWM's may be recovered by performing a printhead maintenance action. Print head maintenance generally includes purging ink through the ink pathways and nozzles of a print head assembly in order to clear contaminants, air bubbles, dried ink, etc. from the print head assembly and/or wiping the nozzle plate of the print head assembly. Printing must typically be stopped and a relatively significant amount of time may be expended while a purging and/or wiping procedure is performed.
Tests have shown, however, that IWM jet failures may recover automatically after a sufficient amount of time has passed (about 30 sec to 2 minutes, for example) without the need of performing a maintenance procedure. Therefore, IWM jet failures may recover without having to stop printing to perform the procedure. Print quality, however, may continue to be impacted while awaiting the automatic recovery of IWM jet failures.